1. Field of the Invention
The present invention generally relates metered dose inhalers (MDIs) and, more particularly, to a single dose MDI for immunizing a patient with a vaccine by inhalation.
2. Description of the Prior Art
Currently, vaccines and other drugs are generally administered to patients by parenteral injection. The chief drawbacks of using injectable vaccines are that the route is invasive and inflicts pain as well as traumatic fright in children and some adults, and that the use of needles necessarily creates a disposal problem with related health hazards such as tuberculosis, AIDS, and other diseases.
Aerosol delivery of vaccines can eliminate both the invasiveness and disposal problems attributed to using injectable drugs. Much work has been done in establishing the efficacy of aerosol delivery of vaccines. For example, Dr. Albert Sabin has been working for several years with aerosol delivery of measles vaccines in third world countries. Even though there have been very effective vaccines for measles for many years, many children in impoverished countries, as well as urban centers in the United States, still die from the disease. Japanese and Russian researchers have also used aerosol delivery of measles vaccines. In addition to measles vaccines, there has been some recent experimentation with the delivery of rubella and attenuated influenza vaccines using aerosol delivery.
An MDI typically comprises a canister under pressure, fitted with a metering valve, which is filled with an aerosol formulation that includes a drug dissolved or dispersed in a propellant together with a surfactant. MDIs are in widespread use in the treatment of chronic disorders such as asthma and the like. The following drugs, as well as many others, are deliverable by MDIs: .beta.-agonists such as albuterol (salbutamol), isoproterenol, ephedrine, epinephrine, salmeterol, terbutaline, and norepinephrine; corticosteroids such as triamcinolone acetonide, beclomethasone diproprionate, dexamethasone, and aldosterone; allergic mediators such as cromolyn sodium; antibiotics; and anticholinergics. MDIs are normally formulated with enough drug for the patient to take several doses of the drug over a given period of the time (e.g., a week, etc.).
Unlike chronic conditions such as asthma which require repetitive dosing of a drug, vaccinating a patient against a disease (e.g., measles, rubella, pertussis, AIDS, influenza, etc.) normally only requires one dose (sometimes two doses given a few months or years apart).